The court martial was in response to the eight charges lodged against Benedict Arnold by Reed and his followers. Arnold demanded satisfaction, but Congress refused to support him, and Reed, I think to purposely torture Arnold, kept asking for delays so he could gather evidence to prove his charges, which makes one wonder why he didn’t seem to have evidence before making the charges (charges filed back in early 1779 but the court martial didn’t take place until Dec. 1780-Jan, 1781).
Benedict Arnold was acquitted of all charges except two: allowing a vessel to clear port in Philadelphia when the port was closed (Arnold had an investment in the vessel and the trade goods it was carrying). And the other charge was using public wagons to move trade goods belonging to him. (Benedict Arnold did acknowledge this charge and was paying for their use).
As for George Washington, he went along with Reed’s incessant delays because Reed kept threatening that he would not call out the Pennsylvania militia to support Washington’s martial efforts if he was not given time to dig up evidence (Washington was actually trying to help Arnold but couldn’t because he thought he needed the troop strength).
The court martial hearing board recommended to Congress that Benedict Arnold be publicly reprimanded and gave the assignment to Washington, who did so only in orders of the day. But that was it. To Arnold, now even Washington seemed like an enemy. Trying to ameliorate matters, Washington offered Arnold command of a wing of the Continental army. But Arnold insisted on the West Point command, and the rest is history.
There was no turning back for Benedict Arnold once that reprimand took place. Disillusionment had morphed into bitterness. Arnold firmly believed that the patriot cause had ruined him and his good name, despite giving his all, including his good health and much of his personal fortune. Stated differently, Arnold believed that Washington and the cause had betrayed him.